Optical Properties of ZnO Hollow Shell Arrays by Nanosphere Lithography (NSL)

초록

Recently, many efforts have been devoted to fabricate the 2D structures into periodic 3D architectures due to the tailoring optical response of these structures. In this work, we fabricated optically active ZnO hollow shells on polystyrene (PS) sphere monolayer using DC magnetron sputtering. PS pattern using 1μm size PS suspension was formed on glass (B270) substrates by the self-assembly method. After that, ZnO was deposited on PS pattern at an oblique angle 65°. Finally, PS spheres were removed by annealing the samples at 500°C in air for one hour. Fig. 1 shows the SEM image of the array of ZnO hollow shells. The light scattering properties of these structures were determined by the optical transmittance spectra. In transmission spectra, several anomalous dips were found, and the dips can be tuned by changing the shell thickness. The various angle reflectance spectra were also measured for ZnO thin films and ZnO hollow shell structures. ZnO hollow shell structure shows a remarkable decrease in the reflectance in the entire vible wavelength range by comparing the ZnO thin films. We also performed a simulation for the transmittance using Finitedifference time-domain (FDTD) method for various schemes such as PS pattern, ZnO/PS pattern and ZnO hollow shell and the results were compared with experimental data.